Interaction between the neuromagnetic responses to sound energy onset and pitch onset suggests common generators A. Seither-Preisler, 1 K. Krumbholz, 1,2 R. Patterson, 3 S. Seither 1 and B. Lu Ètkenho Èner 1 1 Department of Experimental Audiology, ENT Clinic, Mu Ènster University Hospital, Kardinal-von-Galen-Ring 10, D-48149 Mu Ènster, Germany 2 Institute of Medicine, Research Centre Ju Èlich, D-52425 Ju Èlich, Germany 3 Centre for the Neural Basis of Hearing, Department of Physiology, University of Cambridge, Downing Street, CB2 3EG Cambridge, UK Keywords: auditory cortex, auditory evoked ®eld, magnetoencephalography, N100m/ P200m, refractoriness Abstract The pitch-onset response (POR) is a negative component of the auditory evoked ®eld which is elicited when the temporal ®ne structure of a continuous noise is regularized to produce a pitch perception without altering the gross spectral characteristics of the sound. Previously,weshowedthatthelatencyofthePORisinverselyrelatedtothepitchvalueanditsamplitudeiscorrelatedwiththesalience of the pitch, suggesting that the underlying generators are part of a pitch-processing network [Krumbholz, K., Patterson, R.D., Seither- Preisler, A., Lammertmann, C. & Lu Ètkenho Èner, B. (2003) Cereb. Cortex, 13, 765±772]. The source of the POR was located near the medial part of Heschl's gyrus. The present study was designed to determine whether the POR originates from the same generators as the energy-onset response (EOR) represented by the N100m/P200m complex. The EOR to the onset of a noise, and the POR to a subsequenttransitionfromnoisetopitch,wererecordedasthetimeintervalbetweenthenoiseonsetandthetransitionvariedfrom500 to 4000ms. The mean amplitude of the POR increased by  5.9nA.m with each doubling of the time between noise onset and transition. This suggests an interaction between the POR and the EOR, which may be based on common neural generators. Introduction A central function of sensory systems is to extract meaningful infor- mation from noisy backgrounds. The processing is organized hier- archically with elementary stimulus features extracted before more global ones. In the auditory system, this means scanning sounds for regularity in their temporal ®ne structure. Repetitive patterns in the millisecond range produce the sensation of pitch, and detection of pitch initiates pattern analysis on a longer time scale to search for pitch contours typical of melody in music or prosody in speech (Grif®ths etal., 1998; Grif®ths etal., 2001; Patterson etal., 2002). Bilsen (1966) andYost(1996)developedanalgorithmtoregularizethetimeintervals in a noise and produce a Regular Interval Sound (RIS) which has a pitch but which also has the same longer-term spectral characteristics as the original noise. This is achieved by delaying a sample of noise, adding it back to the original, and iterating this delay-and-add process several times. The reciprocal of the delay determines the pitch value and the number of iterations determines the salience of the pitch. In a recent magnetoencephalographic study (Krumbholz et al., 2003) we identi®ed a component of the auditory evoked ®eld which is elicited by the onset of pitch in a continuous sound (pitch-onset response, POR). The stimuli consisted of a 2000-ms segment of noise followed by a 1000-ms segment of RIS without any discontinuity in the sound's temporal envelope or energy. The amplitude of the POR increased with the salience of the pitch (number of iterations) and its latency decreased with the pitch value (1/delay), suggesting that the generators of the POR are involved in pitch processing. The source of the POR was located near the medial part of Heschl's gyrus (HG), somewhat anterior and inferior to the source of the N100m elicited by the energy onset of the noise. The stimulus onset asynchrony (SOA) required to evoke an electro- encephalographic N100 response and its magntoencephalographic counterpart N100m is somewhat less than 500 ms (Nelson & Lassman, 1968; Lammertmann et al., 2000; Onitsuka et al., 2000), and the amplitude of the N100(m) increases with increasing SOA up to  10s. The effect of SOA on N100(m) amplitude probably re¯ects passive refractoriness in the neural generators rather than short-term habitua- tion due to loss of stimulus novelty (Budd et al., 1998). The present study was designed to determine whether there is a similar refractori- ness between the auditory evoked ®eld components associated with energy onset [energy-onset response (EOR): N100m/P200m] and pitch onset in the absence of energy onset (the POR). The stimuli were similar to those in Krumbholz etal. (2003) except that the duration of the noise segment was varied from 500 to 4000 ms. If the POR and the EOR have common neural generators, the POR amplitude should depend on SOA just as the N100m amplitude depends on SOA. European Journal of Neuroscience, Vol. 19, pp. 3073±3080, 2004 ß Federation of European Neuroscience Societies doi:10.1111/j.1460-9568.2004.03423.x Correspondence: Dr A. Seither-Preisler, as above. E-mail: preisler@uni-muenster.de Received 1 April 2004, accepted 8 April 2004